This chapter focuses on postpartum endometritis, especially the role of sexually transmitted organisms or syndromes and the adverse effects of these infections on the reproductive health of young women. Bacteremia is complicated by septic shock in 20 to 50% of medical and surgical patients compared to 0 to 12% of obstetric patients. The mortality rate among endometritis patients with bacteremia ranges from 0 to 4.3%; if septic shock occurs, mortality ranges from 0 to 67%. A large number of risk factors for postpartum endometritis, including labor, rupture of membranes, number of vaginal examinations, use of an internal fetal monitor, low parity, general anesthesia, skill of the surgeons, duration of surgery (>60 min), estimated blood loss (>500 ml), postoperative anemia, positive amniotic fluid culture, vaginal or cervical colonization with a variety of microorganisms including sexually transmitted organisms, absence of amniotic fluid-inhibiting factor(s), failure for labor to progress, and delivery by cesarean section, are evaluated. The use of internal fetal monitoring has been accompanied by concerns about increased intrauterine infection both pre- and postdelivery. The presence of virulent bacteria, including genital mycoplasmas, in the amniotic fluid is a significant risk factor for the development of postpartum endometritis, especially post-cesarean section. The use of antibiotic prophylaxis immediately after cord clamping has been demonstrated to dramatically reduce the incidence of postpartum endometritis following cesarean section. Bacterial vaginosis is a vaginal condition associated with increased concentrations of anaerobic bacteria and G. vaginalis.